Generally, a hydroformylation that is well known an oxo-reaction is a process for producing linear (normal) and branched (iso) aldehydes, in which one carbon number is increased in olefin, by reacting all sorts of olefins with a synthesis gas (CO/H2) under presence of a metal catalyst and ligand. Otto Roelen in Germany originally discovered the oxo-reaction in 1938, and approximately 840 million ton of all sorts of aldehydes (including alcohol derivatives) are produced and consumed through the oxo-reaction all over the world by 2001 (SRI report, November 2002, 682. 700A).
All sorts of aldehydes synthesized from the oxo-reaction are modified to produce acid and alcohol that are aldehyde derivatives through an oxidation or reduction process. Moreover, all sorts of aldehydes synthesized from the oxo-reaction may be modified to produce various acids and alcohols that includes long alkyl group through the oxidation or reduction process after a condensation reaction of aldol, and the like. The alcohols and acids are used as a raw material of solvent, an additive and all sorts of plasticizers, and the like.
A catalyst used for the oxo-reaction is now a type of cobalt (Co) and rhodium (Rh), and N/I (ratio of linear (normal) to branched (iso) isomers) selectivity of aldehyde that is produced is changed by the conditions of operation and type of ligand that is applied. Now, at least 70% of oxo plants in the whole word utilize Low Pressure OXO process that is applied with a rhodium-based catalyst.
Iridium (Ir), ruthenium (Ru), osmium (Os), platinum (Pt), palladium (Pd), iron (Fe), nickel (Ni), and the like may be available to use as a central metal of the oxo catalyst. However, it is known that the order of catalyst activity of metals is Rh>>Co>Ir, Ru>Os>Pt>Pd>Fe>Ni and the like, so that most processes and researches are focused on rhodium and cobalt. Phosphine (PR3; here, R is C6H5 or n-C4H9), phosphine oxide (O═P(C6H5)3), phosphite, amine, amide, isonitride, and the like may be available to apply as a ligand. However, there are few ligands that can be expected to exceed a triaryl phosphine (TAP) in an activity, stability, and a price of catalyst.
Especially, it is known that rhodium (Rh) metal is used as a catalyst and TPP is used as a ligand in most oxo-processes.
It is known that the Rh catalyst is a very expensive metal so that the triaryl phosphine ligand, such as a triphenyl phosphine ligand, should be applied in the amount of at least 100 equivalents based on the Rh catalyst in order to increase the stability of Rh catalyst. However, the ligand equivalent based on the Rh catalyst is increased in order to increase the stability of the catalyst thereby damaging the activity of catalyst so that high concentration of the ligand is also not preferable to use in a commercial aspect.
Today, the industrial importance of a normal aldehyde is significantly increasing so that a catalyst composition having an excellent stability and high activity of catalyst, and high selectivity to the normal aldehyde is urgently required.